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High-risk patients with negative findings at low-dose CT lung cancer screening are still at a high risk of developing lung cancer later in life, according to a new study published in Radiology. The authors added that screening should continue after more than three years.

The authors tracked 200 patients who had negative findings at screening more than three years ago. The average patient age was 74 years old, and the median time since their previous screening was seven years. They all underwent low-dose CT between March 2013 and October 2016.

Overall, lung cancer was detected in 14 of the study’s 200 patients for a detection rate of 7 percent. Twelve of those patients had a stage I or stage II diagnosis, one was stage IIIA and another was stage IV. An additional six patients are undergoing close surveillance imaging due to small partly solid nodules.

“Our study shows that high-risk individuals have a high incidence of lung cancer after previous negative low-dose CT examinations and, therefore, that screening should continue beyond three years,” wrote Heidi Schmidt, MD, of the department of medical imaging at Women’s College Hospital in Toronto, and colleagues. “The definition of the optimum screening interval may be different for various groups of individuals and will be the subject of future studies.”

The authors noted that the older average age of the cohort may be one reason for the lung cancer detection rate (7 percent) being higher than the range seen in previous studies (1.1 to 2.7 percent).